1. Field of the Invention
The present invention relates to a preheaterless manual transfer mold die for encapsulating semiconductor elements in a semiconductor packaging process, and more particularly to a multi-plunger manual transfer mold die which is provided with a multi-plunger assembly instead of one plunger and without a preheater so as to reduce amount of resin used in encapsulation of elements and the curing-time required to stabilize resin, thereby promoting productivity of the mold die.
2. Description of the Prior Art
Referring to FIG. 1, there is shown a conventional manual transfer mold die commonly used in the molding procedure in the process for manufacturing semiconductor packages. As shown in the drawing, the manual transfer mold die may be divided into two main groups, that is, an upper mold die "T" and a lower mold die "B".
The upper mold die "T" comprises a top mold base 1 which is provided with four leader pins 1a at four corners of lower surfaces thereof and a through hole 1b at a center portion thereof, a top center block 2 having a through hole coinciding with the through hole 1b which is fixed to a lower surface of the top mold base 1, top riser blocks 3 and 3' which are divided into front parts and rear parts respectively and mounted on opposite ends of upper surface of the top mold base 1, a top ejector plate 7 interposed between the top riser block 3 and 3' and disposed on the top mold base 1, a top drive plate 6 mounted on the top ejector plate 7, a cylinder plunger bush (or pot) 9 which passes through the top drive plate 6 and the top ejector plate 7 which has an inside hole corresponding to the through hole 1b of the top mold base 1, a plunger 8 adapted to be slidably inserted in the plunger bush 9 by means of a press (not shown), a top return pin 10 fixed to an upper surface of the top mold base 1 which passes through the top drive plate 6 and the top ejector plate 7 and along which the top drive plate 6 and the top ejector plate 7 are slidable, a stud bolt 13 passing through the top drive plate 6 and the top ejector plate 7 which is provided with a spring 14 and engaged with a washer and cushion lock nut 15 at the upper end thereof, a top support pillar 11 mounted on the top drive plate 6, top insulation plates 5 and 5' which are mounted on the front parts and the rear parts of the top riser blocks 3 and 3' respectively, top clamping blocks 4 and 4' which are mounted on the top insulation plates 5 and 5' respectively, and a plurality of screws 12 for assembling the above-mentioned components.
On the other hand, the lower mold die "B" comprises a bottom mold base 21 which is formed with guide holes 21a in which the leader pins 1a formed at the top mold base 1 of the upper mold die "T" are slidably inserted, a bottom center block 22 mounted on the bottom mold base 21 which is formed with a runner 22a and gates 22b at an upper surface thereof, chases 23 which are mounted on both sides of the center block 22 and have a plurality of cavities connected to the gates 22b, bottom riser blocks 24 and 24' mounted on opposite ends of a lower surface of the bottom mold base 21 respectively, a bottom ejector plate 28 which is mounted under the bottom mold base 21 and spaced from the bottom riser block 24 and 24', a spring inserted in a hole 28a formed at an upper surface of the bottom ejector plate 28, a bottom drive plate 27 mounted under the bottom ejector plate 28, a bottom return pin 32 fixed to the bottom drive plate 27 which slideably passes through the bottom ejector plate 28 and has a stopper 33 at lower end thereof, a bottom insulation plate 26 which is mounted on lower surfaces 24 and 24' and under the bottom drive plate 27, a bottom clamp block 25 mounted under the bottom insulation plate 26, a bottom support pillar 30 fixed to the bottom drive plate 27 which is slidably inserted into a through hole 28b of the bottom ejector plate 28, and a plurality of screws for assembling the above-mentioned components.
An operation of the above known manual transfer mold die will be described as follows.
First, preheated lead frames (not shown) are placed in the cavities of the chases 23 mounted on both sides of the bottom center block 22 of the lower mold die "B". Thereafter, the upper and lower mold dies "T" and "B" are clamped by means of the top and bottom clamp blocks 4 and 25. Accordingly, the top center block 2 of the upper mold die "T" is tightly closed to the bottom center block 22 of the lower mold die "B" and the chases 23 mounted on both sides of the bottom center block 22 so that the runner 22a of the bottom center block 22, the gates 22b and the cavities of the chases 23 are sealed.
Subsequently, a massive resin tablet (not shown) is preheated by a high-frequency preheater (not shown) and then put into the plunger bush 9 of the upper mold die "T".
Then, upon pushing a switch of molding press (not shown) related to the plunger 8, the plunger 8 is lowered through the plunger bush 9 so that the resin tablet in the plunger bush 9 is injected into the runner 22a of the bottom center block 22 through the through hole 1b of the top mold base 1. At this time, since the resin tablet is normally preheated to a temperature of 85.degree.-95.degree. C. and the mold die is heated to a temperature of 175.degree..+-.5.degree. C., the resin tablet changes into gel and is injected into the runner 22a. The resin tablet in a gel state is injected into the chases 23 through the gates 22b to fill the cavities of the chases 23.
When the cavities in the chases 23 are completely filled with the resin, the downward movement of the plunger 8 is stopped but the pressurization of the plunger 8 is continuously maintained. Upon being pressurized, the resin is cured. Although the curing time required to cure resin is variable according to desired products, it generally requires a time of 200-300 seconds to cure resin.
When the resin is completely cured, the plunger 8 is raised by the molding press. Thereafter, as the upper mold die "T" is separated from the lower mold die "B", the molded products are raised from the chases 23 by a push pin (not shown) to be removed.
However, when the above-mentioned known manual transfer mold die has a large number of cavities in the chases 23 (for example, the mold die has generally 40-660 cavities), it requires a large amount of resin to mold. Accordingly, resin tablets become large in size because there are only one plunger 8 and one plunger bush 9.
Hence, resin tablets must be put in the plunger bush 9 after being preheated in order to change the resin tablet into gel. Therefore, a preheater must be used in order to preheat the resin tablets, thereby increasing consumption of electric power and necessitating additional space to establish the preheater.
In addition, since resin must be filled in a plurality of cavities through only one runner 22a and then stabilized, it takes a long curing time to stabilize the resin. Also, since the resin tablet must be put in only one plunger bush 9, a large amount of resin tablet must be consumed, thereby decreasing productivity.
Furthermore, since large air gaps are formed between the plunger bush 9 and resin tablet, defects such as foam and porosity and wire sweeping may occur.